Time-restricted feeding (TRF) is becoming a popular way of eating in physically active populations, despite a lack of research on metabolic and performance outcomes as they relate to the timing of food consumption in relation to the time of exercise. The purpose of this study was to determine if the timing of feeding/fasting after exercise training differently affects muscle metabolic flexibility and response to an acute bout of exercise. Male C57BL/6 mice were randomized to one of three groups for 8 weeks. The control had ad libitum access to food before and after exercise training. TRF-immediate had immediate access to food for 6 h following exercise training and the TRF-delayed group had access to food 5-h post exercise for 6 h. The timing of fasting did not impact performance in a run to fatigue despite TRF groups having lower hindlimb muscle mass. TRF-delayed had lower levels of muscle HSL mRNA expression and lower levels of PGC-1α expression but displayed no changes in electron transport chain enzymes. These results suggest that in young populations consuming a healthy diet and exercising, the timing of fasting may not substantially impact metabolic flexibility and running performance.

Intermittent fasting refers to a period of unregulated caloric consumption paired with a period of complete, or heavily restricted, caloric consumption. One version of this involves splitting the day into a consumption period and a restricted period, known as time‐restricted feeding (TRF). TRF is shown to improve metabolic health and positively affect mitochondria, independent of weight loss. Aerobic exercise is also shown to improve these parameters; however, the combination of intermittent fasting and aerobic exercise in a healthy system has not been examined. The purpose of this study was to examine the effects of the feeding window time in relation to exercise on body weight, body fat percentage, lean mass, and run to exhaustion. Healthy, young mice were placed in one of three groups: ad libitum control group (CON), 18‐hour fasting with a 6‐hour feeding starting immediately post exercise (IM), and 18‐hour fasting with a 6 hour feeding starting 5 hours post exercise (DG). The mice ran 5 days a week, 1 hour a day, for a total of 8 weeks at the beginning of the dark cycle. A run to exhaustion (RTE) was conducted at week 0 and week 8 of the study. Mice were weighed twice weekly and underwent an MRI once a week. Data are presented as mean ± SD. A repeated measures two‐way ANOVA was used to compare groups across time. Significance was set a p< 0.05. There were no significant differences between RTE times at week 0 (p= 0.52). There was a main effect of training across all groups in RTE (p=0.04) with a 14±43% increase in RTE in the CON, 13±33% increase in IM, and 55±86% increase in DG. There was a significant increase in body fat in the DG compared to CON at week 2 (CON 7.1±4.5% DG 13.4±2.3%, p=0.002), week 3 (CON 7.2±4.8% DG 11.6±2.6, p=0.02), and week 4 (CON 7.0±4.5% DG 11.6±1.9%, p=0.006); however, there was no difference between groups at week 8. There was a significant effect of time on body weight and lean mass, demonstrating normal growth (p<0.0001). TRF did not have a significant effect (p=0.24) on body weight, however there was a significant decrease in lean mass in TRF groups at week 8 (CON 24.7±2.2g, IM 22.8±2.1g, DG 22.7±1.8g, p=0.03). Although there was a small decrease in lean mass, TRF did not lead to a change in performance as measured by RTE and timing of fasting did not impact either RTE or body composition. This suggests that performance may not be substantially impacted in individuals using TRF, regardless of the timing of the feeding window. Support or Funding Information Funded by the University of Memphis School of Health Studies

Objectives Food intake and exercise are considered modulators of the immune system. Specifically, intermittent fasting protocols have been demonstrated to reduce inflammation and alter cytokine responses. The objective of the current study was to determine if a form of intermittent fasting known as time-restricted feeding (TRF) would alter immune parameters in response to exercise. Methods 8-week-old C57BL/6 male mice were divided into three groups based on feeding schedule; group one had access to food ad libitum (Control) and groups two and three had access to food in a time restricted manner. Access was allowed for six hours per day either immediately after running (TRF-imm) or six hours after running (TRF-del). Mice ran on a treadmill for 1 hour, 5 days per week for eight weeks. Diet consisted of 21% protein, 16% fat and 64% carbohydrate. Weight, glucose and ketone levels, and immune populations were analyzed. Systemic IL-6 and TNF-α levels were measured before and after running. In a subpopulation, cytokine response to lipopolysaccharides (LPS) was also monitored. Results All mice gained weight during the eight-week intervention, but TRF-imm gained significantly less weight than Control (P = 0.02). No differences were detected in glucose levels. The ketone body β-hydroxybutyrate (BHB) was significantly higher at week eight in TRF groups (P ≤ 0.03) but running induced BHB in all groups to approximately 1 mM. Running reduced the blood lymphocytes levels (P &lt; 0.05), with a concomitant increase of granulocytes (P &lt; 0.05) in all groups. There was a small increase in monocytes only in the Control group (P = 0.017). No differences were detected in splenic immune populations, including CD4 and CD8 T cells, and CD11b + cells. Both IL-6 and TNF-α levels were low in all groups before exercise; however, post exercise IL-6 was increased, but not to the same extend in all groups. The IL-6 response was blunted in the TRF groups. The reduced levels of IL-6 was not due to loss of immune function, as both IL-6 and TNF-α were readily induced by exposure of mice to LPS. Conclusions Time-restricted feeding protocols did not induce differences in immune cell composition in blood or spleen but resulted in attenuated exercise-induced IL-6 levels. Funding Sources University of Memphis, School of Health Studies.